The present disclosure relates to unsaturated polyester resins and processes for making the same. In particular, the process for making the resin provides resins with improved properties. The unsaturated polyester resins of the present embodiments can be used as toner resins to prepare toner compositions. In specific embodiments, the toner composition is an emulsion aggregation (EA) toner.
Polyester resins are generally prepared by a polycondensation process involving the reaction of a diol monomer and a diacid or diester monomer and producing water or an alcohol as byproduct, which is collected by distillation. Unsaturated polyester resins can be similarly prepared by this process, with the primary exception that the diacid monomer is unsaturated, that is, it is comprised of an alkene segment such as fumaric or maleic acid or diesters thereof. Electrophotographic toners are generally comprised of a resin, such as a polyester, a pigment and optionally a charge control agent. Many various toner formulations are known, and more specifically, one preferred toner formulation is comprised of a crosslinked unsaturated polyester resin, such that desirable low fixing temperatures and offset properties are attained, reference, for example, U.S. Pat. No. 5,227,460, the disclosure of which is totally incorporated herein by reference, wherein there is disclosed as one preferred unsaturated polyester resin a poly(propoxylated bisphenol co-fumarate) which is crosslinked to a gel content of up to about 40 weight percent utilizing a peroxide to provide a toner useful for electrophotographic processes.
Unsaturated polyester resins derived from propoxylated bisphenol A with fumaric acid are known. More specifically, the propoxylated bisphenol A utilized is comprised for example, of a mixture of monomers prepared by the anionic propoxylation of bisphenol A with propylene oxide, in the presence of an alkali hydroxide catalyst in a pressurized vessel, and wherein the mixtures obtained are the alkali salts of 4-(2-hydroxyethyl)-bisphenol A, bis 4,4′-(2-hydroxyethyl)-bisphenol A, and 4-(2′-hydroxyethyl-2-oxyethyl)-4′-(2-hydroxyethyl)-bisphenol A. There exists, an alternative condensation method of alkoxylation that can be accomplished by the reaction of a diol with a cyclic alkylene carbonate, and specifically wherein bisphenol A can be condensed with a cyclic propylene carbonate in the presence of a catalyst and release carbon dioxide as the byproduct at elevated temperatures, thus producing a mixture of propoxylated bisphenol A. This latter condensation method has numerous economic advantageous in terms of monomer costs, and simplicity.
In U.S. Pat. No. 5,449,719, the disclosure of which, is totally incorporated herein by reference, there is illustrated a two-step process for the preparation of unsaturated polyester resin, and which comprises the first reaction of a phthalate and a glycol to provide a transesterified product, and subsequently a second reaction comprising reacting the product with an unsaturated dicarboxylate monomer. This differs from the present invention in that for example, the first reaction comprises the condensation of a diol with an alkylene carbonate and generates carbon dioxide as the byproduct.
In U.S. Pat. No. 5,407,772, the disclosure of which is totally incorporated herein by reference, there is illustrated an unsaturated linear polyester having repeating units of a reaction product of a first monomer, a second monomer, a third monomer and optionally a fourth monomer. The linear polymers have a glass transition temperature ranging from about 52° C. to about 61° C. average molecular weight less than 200, the second monomer may be a dicarboxylic acid or diester which is different than the third monomer. The concentration of second residues of the polymer, derived from the second monomer, ranges from about 3 weight percent to about 15 weight percent, based on the total weight of the polymer. The third monomer is an aromatic dicarboxylic acid or an ester thereof. The fourth monomer is a diol having a higher molecular weight than the first monomer. In a process for preparing the inventive polymer of '772, the first, the second, the third monomer (and optionally a fourth) and/or a catalyst undergo trans-esterification to form the unsaturated, linear polyester.
In U.S. Pat. No. 4,788,122, there is disclosed the production of a toner polyester resin obtained by co-polycondensation of (a) a diol component of polyalkylene-bis(4-hydroxy-phenyl)propane and (b) an acid component, improved by incorporating into the acid component a copolymer of styrene or derivative thereof and a carboxylic vinyl monomer.
In U.S. Pat. No. 5,466,554, there is disclosed a toner composition with modified polyester resin free of acid end groups, and obtained from the condensation of a first diol monomer, a second diacid monomer and third monovalent alcohol or acid monomer. Similarly, in U.S. Pat. No. 5,686,218 there disclosed a process which comprises reacting a polyester resin end capped with hydroxyl moieties or groups with an organic acid anhydride at a temperature from about 125° C. resulting in a polyester resin end-capped with acid moieties or acid groups. Other polyester based toners and process thereof are illustrated in U.S. Pat. Nos. 4,988,794; 4,727,011; 4,533,614 and 5,366,841.
In U.S. Pat. No. 2,766,292, there is disclosed a process for preparing oxyalkyating derivatives such as anhydrous, substantially undiluted oxyalkylated derivatives from an anhydrous solid, oxyalkylation-susceptible pentaerythritol compound, which satisfies one of the following two conditions (a) it is infusible; (b) it suffers at least partial decomposition if maintained at its beginning of-fusion temperature for a period of at least 15 minutes in the presence of an oxyalkylation catalyst, and which solid is insoluble in oxyalkylation-resistant, distillation separable solvent; which process consists of reacting the solid with at least one alkylene carbonate selected from ethylene carbonate, propylene carbonate, and butylene carbonate, in the presence of an oxyalkylation catalyst at a temperature producing carbon dioxide.
In U.S. Pat. No. 4,131,731, there is disclosed a process for preparing linear polycarbonates containing terminal hydroxyl groups with the essential exclusion of other terminal groups by reacting glycols having a carbon number greater than 4 and cyclic esters of carbonic acid via ester interchange reaction at 100° C. to 300° C. and 0.1-300 mm Hg.
In U.S. Pat. No. 5,373,030 there is disclosed a process for the preparation of polyurethane foams and similarly, in U.S. Pat. No. 5,332,860 there is illustrated the use of polyols for preparing polyurethane foams having improved retention of insulative properties.
In U.S. Pat. No. 5,714,568 there is disclosed a process comprising the reaction of a polyfunctional organic acid or anhydride and a cyclic organic carbonate compound in the presence of a catalyst selected from the group consisting of an alkali metal, thereby generating a polyester or copolyester resin.
Japanese Patent Publication JP 10077336 A2 discloses a process for the preparation of copolyesters by the reaction of an aromatic diol with an alkylene carbonate in the presence of an alkali carbonate catalyst to form a diol, at a conversion of, for example, more than about 75 percent as measured by the evolution of carbon dioxide byproduct, followed by the subsequent addition of yet another diol and a diacid and continuing the polymerization at high pressure and temperature of about 240 yield the aforesaid copolyester resin. The isomeric mixtures in the present invention comprised, for example, of isomers I, II and III are not believed to be disclosed in the JP '336 documents particularly in the isomer ratios of from about 0 to about 5 weight percent of isomer I, of from about 89 to about 97 weight percent of isomer II, and from about 0 to about 15 weight percent of isomer III, by the utilization of a mixture of both an alkali carbonate and an alcohol. The process of the present invention differs, for example, in that the specific mixtures amounts of the three isomers are controlled and obtained by the use of specific catalyst in a multistep process to form polyester resins that can be selected for use as toner binders. Furthermore, the unsaturated polyester, poly(propoxylated bisphenol A—co-fumarate) is not apparently disclosed in the above JP '336 document. The unsaturated polyesters of the present invention are of importance for crosslinking to a high gel content of for example, from about 5 to about 50 percent gel. Additionally, in the process of the present invention, high pressures are not necessarily utilized in forming the polyester resins, and in embodiments the highest temperature selected to generate the polyester resin is from about 200° C. JP '336 patent utilizes both a diol and diacid during the polymerization steps to form a copolyester. This differs from the present invention wherein in embodiments a diacid is utilized to form the polyester during the polycondensation step.
Japanese Patent publication JP 10095840 A2 discloses a process for the preparation of copolyesters by the reaction of an aromatic diol with an alkylene carbonate in the presence of an alkali carbonate catalyst to form a diol, at a conversion of for example, more than about 75 percent as measured by the evolution of carbon dioxide byproduct, followed by the subsequent addition of yet another diol and a mixture of diacid and continuing the polymerization at high pressure and temperature of about 240° C. mixtures in the present invention are comprised of isomers I, II and III which do not appear to be recognized or disclosed in the JP '840 documents, particularly in a three step monomer processes to produce the isomer ratios of from about 0 to about 1 weight percent of isomer I, of from about 89 to about 97 weight percent of isomer II, and from about 3 to about 15 weight percent of isomer III, by the utilization of a mixture of both an alkali carbonate and alcohol derived alkali. Furthermore, the aforementioned '840 patent utilizes both a diol and diacid during the polymerization steps to form a copolyester. This differs from the present invention wherein in embodiments only a diacid need be utilized to form the polyester during the polycondensation step.
Japanese Patent Publication JP 10087802 A2 discloses a process for the preparation of polyesters obtained by polymerizing an aromatic dicarboxylic acid and aliphatic glycol to form a carboxylic group-terminated polyester oligomer with esterification degree of about 80 percent conversion, and melt reacting with an aromatic diol and cyclic 5 or 6 member alkylene carbonate in the presence of a catalyst such as lithium diacetate. It is a feature of the present invention to provide economical process for the preparation of polyester resins.
It is desirable to use a multistep “one pot” economical process for the preparation of polyester resins, such as an unsaturated polyester resin. While such processes have been devised, such as described in U.S. Pat. Nos. 8,466,254, 6,063,827 and 6,127,080, which are hereby incorporated by reference in their entireties, it has been discovered that producing such polyester resins for use in toners on a large scale, such as during commercial manufacturing, have shown to contain unacceptably high levels of particle fines. Particle fines are those considered too small, and are in the size range of from about 1.4 to about 3.17 microns. High levels of particle fines are undesirable as they hinder toner performance and can lead to poor imaging quality. Extensive analysis revealed that unreacted fumaric acid in the resin caused the formation of particle fines.
Thus, there is a need to optimize the resin formulation and process to address these issues and provide improved toner performance.